Originally Posted by ad_infinitum
Originally Posted by Whammo
Originally Posted by ad_infinitum
No. It means that it flows well at low temperature, and doesn't lose viscosity dramatically at operating temperature.
For comparison, Mobil 1 0w-20 AFE's viscosity index is 173, 5w-30 is 172, and 10w-30 is 146.
Okay, so it isn't saying that it is thicker than the others at operating temperature?
Maybe this chart can help you understand: at 40c all the oils are the same viscosity, but as the temperature increases the oils with a lower VI lose their viscosity at a more significant rate in comparison to the oils with a higher VI.
Seems like the oil with the higher VI keeps its true thickness better at engine temperature, thus producing the better oil than the lower VI oil.
HTHS is still the best oil spec to go by, for usefulness at temp in an engine.